\begin{tikzpicture}
	\pgfmathsetmacro{\r}{1.5}
	\pgfmathsetmacro{\a}{45}
	\tkzDefPoints{0/0/O}
	\tkzDefPoint(\a:\r){C}
	\tkzDefPoint(90+\a:\r){A}
	\tkzDefPoint(180+\a:\r){D}
	\tkzDefPoint(270+\a:\r){B}

	\tkzDrawSegments(A,B  C,D)
	\tkzMarkRightAngle(B,O,C)
	\tkzLabelPoints[below](A,B,C,D)
	\tkzLabelPoints[left](O)
\end{tikzpicture}

